Brain tumors remain one of the most challenging forms of cancer despite continuing advances in diagnosis and treatment. Improved therapies will require a greatly-improved understanding of how specific genetic alterations can lead to the development and growth of brain tumors. We are seeking to develop an improved model system in which normal human astrocytes can be transformed through the introduction of defined genetic alterations to analyze the biologic alterations caused by these changes. An analysis of the genetic alterations frequently found in human brain tumor samples allows for the development of a set of targets that are likely required for alteration in the transformation of the normal precursor cell for astrocytomas, the astrocyte. Our hypothesis is that the transformation of normal human astrocytes into gliomas can be modeled by a restricted set of minimal required genetic alterations and that targeting of these pathways will permit the development of therapies useful in a broad range of gliomas. We plan to use the previously established system of amphotropic retroviruses with SV-40 large T antigen, hTERT, and HrasV12G to transform human astrocytes. Our Specific Aims include to determine: 1) if large T antigen, hTERT, and HrasVl2G are sufficient to transform human astrocytes and measure genomic instability and gene expression changes, 2) the relative importance of different rasactivated pathways in astrocyte transformation, 3) if a constitutively active EGF receptor mutant is sufficient to replace activated ras in transforming astrocytes, 4) the effect of TGF beta expression on tumor growth and development, 5) if the loss of the tumor suppressor gene Pten is sufficient to activate ras pathways to permit transformation, and 6) if pathway-specific inhibitors can prevent astrocyte transformation and tumor growth.